The present invention relates to telecommunication systems, in particular WLL systems.
WLL system (WLL, Wireless Local Loop) refers to a system in which a subscriber is connected to a telephone network via a wireless link system. The wireless link system can be implemented using mobile communication technology, such as GSM technology (GSM, Global System for Mobile communications). The subscriber interface is implemented using a special telecommunication terminal.
In a WLL system, the subscriber""s telecommunication terminal is connected via a radio link to a telephone exchange or an access node. Between the telecommunication terminal and the telephone exchange or access node there is a base station, by means of which call signals received from the telecommunication terminal by radio are transmitted via the telephone exchange or access node further to the public telephone network and vice versa. The access node is connected to the telephone exchange e.g. using a V5.1 or V5.2 protocol.
Open interfaces (V5.1 and V5.2) between an access node and a telephone exchange are defined in the ETSI (European Telecommunications and Standards Institute) standards. V5 interfaces enable subscribers belonging to a physically separate access network, which may be a wired or a wireless network, to be connected using a standard telephone exchange interface.
Call tracing is a necessary function in the WLL system. Tracing is used to collect information about call-time events related to a given subscriber, such as the radio channel used, power level, location, call setup direction, duration or start time. The call tracing function can be used to locate faults in the wireless link system, to locate stolen terminals or mischief caused in the network via a terminal, or to prevent illicit use of a terminal.
Previously known tracing methods used in the GSM system are those based on IMSI and IMEI. According to its definition, IMSI (International Mobile Subscriber Identity) is a code consisting of the mobile subscriber""s national identity code and a mobile communication country code, allowing unambiguous identification of the mobile subscriber. Where card-controlled telecommunication terminals are used, the international mobile subscriber identity code is card-specific, in other words, the user is identified on the basis of the SIM card (SIM, Subscriber Identity Module) placed in the telecommunication terminal and not on the basis of the terminal device itself. IMEI (International Mobile station Equipment Identity) is a code by which the telecommunication terminal can be unambiguously identified. The ETSI standard describes both IMSI and IMEI based tracing methods. Managing all the information generated as a result of different types of tracing is a complicated task which occupies resources of both the network management system and the operator. The operator must have separate means for IMSI and IMEI tracing procedures. Thus, both the means and the associated training for their use are a source of expenses to the operator.
The object of the present invention is to solve the problems described above. A specific object of the invention is to disclose a new type of method and system for tracing subscriptions in a WLL system.
The invention relates to a method for tracing a subscription in a telecommunication system comprising a local exchange, an access node connected to the local exchange, a wireless link system connected to the access node and a telecommunication terminal connected to the access node via the wireless link system. Moreover, an IMEI code corresponding to the telecommunication terminal and an IMSI code corresponding to the subscriber are defined in the telecommunication system. In the method of the invention, the access node starts the tracing of a subscription on the basis of the IMEI code and converts the tracing into an IMSI tracing procedure, so that the means intended for tracing in the access node only see the IMSI tracing procedure. In an embodiment of the invention, a reference number is generated on the basis of IMEI tracing and this number is linked with the IMSI tracing. The IMEI tracing is preferably activated for a telecommunication terminal listed in the equipment register of the access node as a device to be traced.
In a preferred embodiment, a tracing report is generated which comprises the IMEI code, IMSI code and reference number. The IMSI code corresponding to the IMEI code is preferably retrieved from a subscriber data register. The IMSI code may also be taken from the call initiating messages. In an embodiment, an alarm is generated in conjunction with a call by a terminal without a subscriber identity module, in which case e.g. the IMEI code, location area and call event of the telecommunication terminal are presented in conjunction with the alarm.
In an embodiment of the method, the wireless link system is based on a digital mobile communication system, such as the GSM system.
Moreover, the invention concerns a system for the tracing of a subscription in a telecommunication system as described above. In the system of the invention, the access node comprises means for tracing a subscriber on the basis of the IMEI code and means for converting the tracing into an IMSI tracing procedure. In an embodiment, the access node comprises means for generating a reference number based on IMEI tracing and for linking the reference number with the IMSI tracing procedure. The access node preferably comprises an equipment register in which the telecommunication terminal subject to IMEI tracing is entered.
In a preferred embodiment of the system, the access node comprises means for generating a report. The report may include the IMEI code, the IMSI code and the reference number. A system according to the invention comprises a subscriber data register comprised in the access node, said register containing the IMSI code corresponding to the IMEI code. The access node preferably comprises means for obtaining the IMSI code from the call initiating messages, allowing it to be transferred to the subscriber data register.
In an embodiment, the access node comprises means for generating an alarm from a call by a telecommunication terminal without a subscriber identity module, the alarm comprising e.g. the IMEI code and location area and call event of the telecommunication terminal.
In an embodiment of the system, the wireless link system used is based on a digital mobile communication system, such as the GSM system.
The invention allows easier processing of the tracing data collected by an access node because it is now possible to utilize IMSI tracing operations and means. In the system, there is no need for separate IMEI tracing follow-up processing and associated equipment. In this way, system capacity is made available for other operations and efficiency is maximized. In addition, the consistency in IMEI and IMEI tracing procedures renders the operator""s work easier.